The present invention relates to divalent silver (AgII) halide bactericides. The bactericidal properties of soluble Ag(II) compounds is the subject of U.S. Pat. No. 5,017,285 of the present inventor. In said patent the inventor described the preparation of soluble Ag(II) compounds which are effective bactericides in swimming pool and industrial cooling tower waters. These compounds are prepared by dissolving divalent silver oxide, AgO, in certain acids such as phosphoric acid, which form stable Ag(II) complexes. In the course of experimenting with these complexes, it was found that halides precipitated Ag(II) halides from these solutions. It should be noted that the solubility of Ag(II) compounds is totally unrelated to those of Ag(I) in water. For example, Ag(II) sulfate is totally soluble compared to the partially soluble Ag(I) salt. Thus the fact that Ag(II) precipitates halides is not necessarily to be anticipated since the Ag(I) and Ag(II) chemistries are different and distinct despite the fact that they represent dissimilar states of the same element. It was also found that Ag(II) complexes had a greater tolerance for free halide in solution than Ag(I). Accordingly, water sources containing 100 PPM of dissolved sodium chloride (NaCl) would not precipitate insoluble chloride from those solutions which are described in my aforementioned patent. However, water with substantially higher halide content precipitated silver halide.
It was postulated that for those high halide waters, such as sea water used for swimming pools, brackish waters used in cooling towers, swimming pools maintained with calcium chloride for mineralization or mineralized hot tubs, Ag(II) halides could be useful provided they exhibited bactericidal properties since they are already insoluble and will not be prone to precipitation. This was highly desirable since tests conducted in a swimming pool with a high chloride content produced an aesthetically unacceptable curdy white precipitate of chloride when it was treated with an Ag(II) phosphate complex. Of course, since a divalent silver halide is effective and would by necessity have to be produced from a soluble bactericidally active Ag(II) complex, it would not be the first product of choice for low-salt or salt-free water treatment where said soluble Ag(II) complexes were the preferable product. However, there existed the possibility that direct action of a hydrohalic acid on AgO could yield end product Ag(II) halides even though the latter were insoluble. If this were possible, then said Ag(II) halides would be intrinsically competitive with the soluble Ag(II) complexes. Accordingly, it was found that Ag(II) halides are bactericidally active and that they could be prepared both directly and indirectly from AgO.